Answers

Background is I'm organizing a LAN-Party with about 300 users. We have quite a good internet connection, but I'd like to reduce traffic as much as I can, to not disrupt online gaming.

Maybe the better question is what the hell WSUS has to do with a gaming LAN-party?

Even *IF* you were to configure them all to use your WSUS server:

It would be pointless because of the amount of TIME and EFFORT it would take to download and install the missing patches.

Doing so is a violation of the EULA for WSUS and for Windows Server!

If you want to require that your party attendees have a fully-patched computer before connecting to your LAN then just have 'em boot up the computer (OFF of the network) and prove to you that updates were installed since the last Patch Tuesday. If they
were, they probably got all of 'em; if they weren't, then don't give 'em a port!

Click Enabled and type the HTTP(S) URL of the same WSUS server in the
Set the intranet update service for detecting updates box and in the
Set the intranet statistics server box. For example, type
http(s)://servername in both boxes, where servername is the name of the server. If the port is not 80 for HTTP or 443 for HTTPS, you should add the port number:
https://servername:portnumber.

If you have no access and no GPO then I suppose supplying a registry file and asking everyone to load it is out of the question too - http://technet.microsoft.com/en-us/library/cc708449%28v=ws.10%29.aspx

A second registry setting to restore the old environment after than LAN party would be needed too.

Background is I'm organizing a LAN-Party with about 300 users. We have quite a good internet connection, but I'd like to reduce traffic as much as I can, to not disrupt online gaming.

Maybe the better question is what the hell WSUS has to do with a gaming LAN-party?

Even *IF* you were to configure them all to use your WSUS server:

It would be pointless because of the amount of TIME and EFFORT it would take to download and install the missing patches.

Doing so is a violation of the EULA for WSUS and for Windows Server!

If you want to require that your party attendees have a fully-patched computer before connecting to your LAN then just have 'em boot up the computer (OFF of the network) and prove to you that updates were installed since the last Patch Tuesday. If they
were, they probably got all of 'em; if they weren't, then don't give 'em a port!

Microsoft is conducting an online survey to understand your opinion of the Technet Web site. If you choose to participate, the online survey will be presented to you when you leave the Technet Web site.